Abstract

Transient elevation of the ST segment in alternate beats of an ECG is reported in two patients during episodes of Prinzmetal angina. Coronary arteriography showed severe three-vessel disease and 90% narrowing of the main left coronary artery in one patient with ST-segment elevation in V1 to V4 but only 50% narrowing of the left circumflex in another patient with ST elevation in Lead I. Similar ST-segment alternans has been reported in dogs during coronary artery ligation. Failure of an ischemic area to depolarize on alternate beats or regional ischemia causing alternation of the amplitude of transmembrane action potentials are possible mechanisms.